WHALES SNOOZE HALF A BRAIN AT A TIME
02.9.08 - Leído 83 veces. Enviar esta notaJennifer Viegas
Sperm whales literally drift to sleep, but it’s a snooze like no other, according to a recent study that found whales perform slow, rhythmic dives as they slumber
WASHINGTON, US; February 9, 2008.- Because these drift dives keep the whales in constant motion as they rest, scientists now think the seafaring mammals sleep with one side of their brain at a time. The two sides alternate until both are rested.
Sperm whales might even break a world record for least amount of sleep needed by a mammal.
“If the only sleep sperm whales get is during these drift dives, it would be less than any mammal studied so far,” lead author Patrick Miller told Discovery News.
Miller, a senior research fellow at the University of St. Andrews Gatty Marine Research Institute, and his colleagues affixed suction cups with data-logging tags onto 59 sperm whales at various open-water locations worldwide. The tags allowed the scientists to monitor the whales’ movements 24/7.
The researchers, whose study was recently published in Current Biology, noticed the whales performed the mesmerizing drift dives 7.1 percent of the time, usually between 6 p.m. and midnight.
The scientists observed two types of drift dives. The first, head-up drift dives, happen when a whale’s rear end slowly sinks into the water from a horizontal posture.
During the second type, head-down, the whale descends slowly with its head directed toward the ocean floor. It travels downward about one or two body lengths in depth before flipping back upward toward the water’s surface. The researchers think the whale’s internal buoyancy causes this natural upward motion, similar to how a sinking apple eventually bobs back to the surface.
“Because the drift dives are quite short (averaging around 12.7 minutes in duration) and are broken by the need for the whale to move to the surface to breathe, it seems that they sleep over short interrupted periods,” said Miller.
“Cat naps for sperm whales, perhaps?” he suggested.
The scientists made the connection when one of their vessels, off the coast of northern Chile, nearly crashed into a group of seemingly oblivious sperm whales. Terrified and in tears, one of the researchers captured the harrowing moment on video.
The boat, under sail power alone, unintentionally touched one of the whales. Only then did the whale seem to wake up and flee, along with its companions. Still photography shows the vessel was in eye-shot of the whales, but the researchers now suspect that side of the whales’ brains might have been in dreamland at the time.
The findings support other research that whales and their kin aren’t exactly heavy sleepers.
Dolphins and killer whales don’t seem to sleep at all during their first month of life, according to Jerome Siegel, director of the Center for Sleep Research at the University of California at Los Angeles. Siegel and his colleagues drew that conclusion after observing killer whales and their calves at SeaWorld San Diego and mother dolphins and their calves at two public sites in Russia’s Black Sea.
Since the young cetaceans don’t appear to sleep at all during this period, the mothers also seem to get very little rest.
“Somehow these seafaring mammals have found a way to cope with sleep deprivation, facilitating rather than hindering a crucial phase of development for their offspring,” said Siegel.
“Their bodies have found a way to cope, offering evidence that sleep isn’t necessary for development, and raising the question of whether humans and other mammals have untapped physiological potential for coping without sleep,” he added.
(Discovery News)
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